1. Field of the Invention
The present invention relates to a vibration wave motor and, more particularly, to a vibration wave motor wherein an elastic member in which a travelling wave is generated is urged against a rail-like stationary member, and is moved along the rail-like stationary member, and to a printer using the vibration wave motor.
2. Description of the Related Art
A conventional vibration wave motor of this type is proposed in U.S. Pat. No. 5,192,890. FIGS. 11 and 12 show the motor.
An elastic member 1 consists of a metal material, and has a projection 1a formed on the sliding surface side. When an AC voltage is applied to a piezoelectric element 2 joined to the upper surface of the elastic member 1, a travelling vibration wave is generated in the elastic member 1. Since the generation principle of the travelling vibration wave and the structure of the piezoelectric element 2 are known to those who are skilled in the art, a detailed description thereof will be omitted. Generally, the travelling vibration wave is formed when AC voltages having a temporal phase difference of 90.degree. are applied to two groups of driving piezoelectric elements which are positionally shifted by 90.degree. of the piezoelectric element. A rail-shaped stationary member 8 frictionally contacts the elastic member 1, and is fixed to a bottom plate 10 of a motor case. More specifically, the elastic member 1 is biased to contact the stationary member 81 via a vibration insulating member 6 (e.g., felt) and a compression spring 3.
A planar auxiliary supporting member 7 has an H shape when it is viewed from the top (see, e.g., FIG. 12), and is joined to the bottom portion of a slit of the elastic member 1. The supporting member 7 firmly supports the central portion of the elastic member 1 to a table 4. Thus, the elastic member 1 can make a smooth linear motion together with the table 4 without cluttering.
This motor is used for driving a printing head in, e.g., a bubble-jet printer. The printing head is mounted on a carriage (not shown) attached to the table 4, and the motor linearly and reciprocally moves the printing head.
However, it is very difficult to accurately bring the elastic member 1 into surface-contact with the rail-shaped stationary member 8 due to dimensional errors of parts, and the like. In practice, as shown in FIGS. 13 and 14, the elastic member 1 may contact the stationary member 8 at an oblique angle. For this reason, the contact state between the elastic member 1 and the rail-shaped stationary member 8 becomes line contact and unstable. When the contact state changes in the moving direction of the elastic member 1, it is difficult to stably move the elastic member 1.
Such problems of the vibration wave motor impair print precision of the printer.